Conventional belt conveyors use idlers to support the length of the belt. The trough formed by the idlers and belt typically has a V-shape cross section for holding the material being carried along the belt conveyor. The V-shape cross section disadvantageously creates a pinch point at the bottom of the V-shape. Conventional belt conveyors also disadvantageously have belt sag between idlers and idler bumping causing material to be thrown up every time it goes over an idler, resulting in dust generations, product separation and degradation.
At the loading zones where material are loaded onto a belt conveyor, impact resulting from lump size, material density and height of material free fall could seriously damage the belt. In a conventional belt conveyor system, at the impact section, impact idlers are used. Impact idlers are generally cushioned to sustain the impacting force of dropped objects.
The vertical velocity of the material dropped from various heights above the belt surface and the horizontal belt speed will be different than the speed of the material when it contacts the belt, resulting in greater impact and shearing forces on the belt. Lumpy materials can cause appreciable impact on the belt. The heavier the lump, the greater height of fall or the greater its angular velocity when it contacts the belt, the greater will be the energy tending to rupture the belt. When the material strikes the belt directly over a conventional belt conveyor with idlers, damages to the carcass can result from the crushing action of the lump against the idlers.
Air supported belt conveyors (ASBC) overcome many of the disadvantages of conventional belt conveyors. As shown in FIG. 1, an ASBC 1 includes a large air chamber 2 with a curve plenum plate 3 forming the upper section of the air chamber 2. Along the length of the plenum plate 3 are a plurality of holes 4. A plenum bed 5 (i.e. belt) rests on top of the plenum plate 3 for holding the material 6 being carried along the ASBC. An ASBC may optionally include a roof cover (not shown). When air is blown into the air chamber 2, air travels through the holes 4 forming a film of air between the plenum plate 3 and plenum bed 5. The entire length of the plenum bed 5 and load of the ASBC is fully supported by a thin cushion of air and advantageously prevent belt sag and idler bumping of conventional belt conveyors. The curvature of the plenum plate 3 and plenum bed 5 also advantageously avoid pinching as in conventional belt conveyors. Further, the lack of idlers produces less friction than conventional belt conveyors. Because impact idlers are not used, there is a need for an improved impact section at the loading zone of an ASBC to minimize damage to the ASBC.